whatever I use nuun tablets because they’re about the lowest amount of sugar I could find, but still 15 calories, so they’ll technically break a fast. I guess it depends on why you’re fasting and how much that matters. If you’re doing 16/8s for weight loss, it won’t matter much. If you’re on day 3 and looking for autophagy benefits, it won’t work.
If you need to be super strict, just take magnesium and potassium supplements along with salted lemon water, that’s probably the easiest solution.